Polymeric organic materials that typically are used to make optical elements, transparent sheets and films, often have surfaces that are susceptible to abrasion and chemical attack. To prevent damage, such materials may be coated with a protective coating to improve their abrasion resistance.
Numerous protective coatings of various chemistries have been developed in the optical art. For example, coatings that incorporate epoxy-containing silane monomers, aluminum compounds and other silane monomers have been described in the literature. Coatings prepared from a colloidal dispersion of a water-insoluble dispersant such as aluminum oxide in a water-alcohol solution of selected organotrialkoxysilanes have also been developed. Hard coat compositions such as epoxy group-containing difunctional alkoxysilanes, tetrafunctional silanes, colloidal titania or alumina and curing catalysts are also among the conventional systems. While each of these coatings provides adequate abrasion resistance to plastic substrates, the abrasion resistance of glass is still much greater than that of hard-coated plastic and is the ideal. Abrasion resistance approaching that of glass is particularly desired in rigorous environments such as those mobile phones, touch screens, and the like are exposed regularly.
It would be desirable to provide articles having coatings that provide abrasion resistance approaching that of glass while allowing for lower cost, light weight, impact performance, moisture barrier and easy removal.